The present invention relates to a plant for liquefying natural gas.
A plant for liquefying natural gas comprises a main heat exchanger in which the natural gas is liquefied by means of indirect heat exchange with evaporating refrigerant, and a refrigerant circuit in which evaporated refrigerant is compressed and liquefied to produce liquid refrigerant that is used in the main heat exchanger. The refrigerant circuit includes a compressor train consisting of at least one compressor. The at least one compressor is driven by means of a gas turbine that is directly connected to the shaft of the compressor. Such a plant is disclosed in U.S. Pat. No. 5,689,141. Because a gas turbine has only a limited operating window, the gas turbine is first selected and the liquefaction plant is so designed that the gas turbine operates in its limited operating window. In addition the gas turbine and the compressor are directly connected to each other, so that they form a single unit. The single unit occupies a considerable surface area.
There is a tendency to look for ways of reducing the surface area of such a liquefaction plant. This does not only apply to on-shore plants, but also to floating liquefaction plants.
Such floating liquefaction plants are used in the development of off-shore gas fields, where the gas is liquefied near the production location. Thereto the liquefaction plant is installed on a barge that serves as a floating storage of liquefied natural gas. The barge is furthermore provided with an off-loading system to transfer the liquefied natural gas into a tanker, and with a gas loading system that is connected by means of a swivel to the upper end of a riser pipe, wherein the lower end of the riser pipe is connected to a well producing natural gas.
It is an object of the present invention to provide a plant for liquefying natural gas that is flexible and that occupies a small surface area, so that, for example a barge can accommodate the liquefaction plant.
To this end, the plant for liquefying natural gas according to the present invention comprises a main heat exchanger in which natural gas is liquefied by means of indirect heat exchange with evaporating refrigerant, and a refrigerant circuit in which evaporated refrigerant is compressed and liquefied to produce liquid refrigerant that is used in the main heat exchanger, wherein the refrigerant circuit includes a compressor train consisting of at least one compressor driven by an electric motor.
It will be understood that there should be provided an electric power plant to provide electric energy to drive the electric motors. The electric power plant will include one or more gas or steam turbines each driving an electric generator. With the liquefaction plant according to the present invention, the gas or steam turbine(s) can be put everywhere where for reasons of lay-out planning or for reasons of safety they are best located.